world_pos = self._view_state.DisplayToWorld(pos)
self._game_state.AddEntity(Unit(world_pos))

if not self.__current_operation:
            for operation in self.__operations:
                if operation.TestBegin(self.__input_state):
                    self.__current_operation = operation
                    break

        view_state.RenderBackground(surface)    
        game_state.Render(surface, view_state, _GLOBAL_SELECTION_SET)
        view_state.RenderForeground(surface)
    
        
    def Render(self, surface, view_state, selection_set):
        for entity in self._entities:
            entity.Render(surface, view_state, 
                          selected=entity in selection_set)